In medical fields, radiation emission computed tomography (ECT: Emission Computed Tomography) apparatus is used that detects an annihilation radiation pair (for example, gamma rays) emitted from radiopharmaceutical that is administered to a subject and is localized to a site of interest for obtaining sectional images of the site of interest in the subject showing radiopharmaceutical distributions. Typical ECT apparatus includes, for example, a PET (Positron Emission Tomography) device and an SPECT (Single Photon Emission Computed Tomography) device.
A PET device will be described by way of example. The PET device has a group of detectors having block radiation detectors arranged in a ring shape. The group of detectors is provided, for surrounding a subject, and allows detection of an annihilation radiation pair that is transmitted through the subject.
First, description will be given of a configuration of a conventional PET device. As shown in FIG. 18, a conventional PET device 50 includes a gantry 51 with an introducing hole that introduces a subject, a group of detectors 53 having block radiation detectors 52 for detecting radiation being arranged inside the gantry 51 so as to surround the introducing hole, and a holding member 54 provided so as to surround the group of detectors 53. Each of the radiation detectors 52 has a bleeder unit 55 with a bleeder circuit in a position between the holding member 54 and thereof for connecting the holding member 54 and the radiation detector 52. The bleeder unit 55 is coupled to a light detector 62, mentioned later, in the radiation detector 52.
Such radiation detector arranged in the group of detectors of the PET device is often equipped that allows position discrimination in a depth direction of a scintillator provided in the radiation detector for improved resolution. Next, description will be given of a construction of the radiation detector 52. As shown in FIG. 19, the conventional radiation detector 52 includes a scintillator 61 that converts radiation into fluorescence, and a photomultiplier tube (hereinafter referred to as a light detector) 62 that detects fluorescence. The scintillator 61 has scintillation counter crystals 63 of rectangular solid that are arranged in a two-dimensional array. The light detector 62 allows discrimination about which scintillation counter crystal 63 emits fluorescence. That is, the radiation detector 52 may discriminate an incidence position of radiation in the scintillator 61. A light guide 64 is provided between the scintillator 61 and the light detector 62 for receiving fluorescence.
Here in the PET device 50, the radiation detectors 52 in the group of detectors 53 have to be arranged precisely. The PET device 50 acquires a sectional image based on an incidence direction of radiation. Accordingly, when a deviation occurs in arrangement of the radiation detectors 52 in the group of detectors 53, the deviation also influences the sectional image acquired with the PET device 50. Specifically, where the radiation detectors 52 in the group of detectors 53 are not positioned as they are by an original setting, the incidence position of radiation determined with the group of detectors 53 deviates from an actual incidence position thereof even when localization of radiopharmaceutical in the subject is identified from data that is outputted from the group of detectors 53. Thus, the conventional PET device 50 has a configuration in which the holding member 54 is divided into split sections, and the radiation detectors are loaded therein in order that the radiation detectors 52 are regularly arranged to the extent possible (see, for example, Patent Literature 1.)